docs: def get_unit_hostnames(self, units):
          """Return a dict of juju unit names to hostnames."""
          host_names = {}
          for unit in units:
              host_names[unit.info['unit_name']] = \
                  str(unit.file_contents('/etc/hostname').strip())
          self.log.debug('Unit host names: {}'.format(host_names))
          return host_names